The present invention relates to a fuel injection control method and a system thereof, and more particularly, to a fuel injection pressure control method and system for reducing an unnecessary power loss of an engine by controlling an output pressure of a high-pressure pump.
Generally, a compression ignition engine is provided with a fuel injection control system for controlling the pressure of injected fuel. Also, a gasoline direct injection (GDI) engine is provided with a fuel injection control system.
As shown in FIG. 3, a fuel injection control system may include a fuel rail 103 to which a plurality of fuel injectors are connected, a high-pressure pump 101 for pumping fuel into the fuel rail 103, a fuel pressure sensor 109 for detecting pressure of fuel inside the fuel rail 103, and a fuel-pressure control valve 107 for controlling pressure of fuel. The fuel-pressure control valve 107 is mounted to the fuel rail 103. An engine control unit (hereinafter referred to as an ECU) generates a fuel return signal for returning some portion of fuel of the fuel rail 103 to the high-pressure pump 101.
If the fuel-pressure control valve 107 is operated according to the fuel return signal, some portion of fuel of the fuel rail 103 returns to the high-pressure pump 101 so that pressure of fuel injected from the fuel injector 105 is regulated.
In the fuel injection control system according to the prior art, the high-pressure pump 101 pressurizes fuel without regard for an amount of fuel injected from the fuel injector 105, and the fuel-pressure control valve 107 returns some portion of fuel being pressurized by the high-pressure pump 101 to the high-pressure pump 101. Therefore, a high load on the output port of the high-pressure pump 101 is maintained. As a result, an engine loss for operating the high-pressure pump 101 is increased.
The present invention provides a fuel injection control system for controlling an output pressure of an output port of a high-pressure fuel pump on the basis of operating conditions of a vehicle such that engine power loss caused by an unnecessary operation of the high-pressure pump is reduced in order to increase fuel economy.
In a preferred embodiment of the present invention, a fuel rail to which a plurality of fuel injectors are connected is provided. A high-pressure pump pressurizes fuel and provides the pressurized fuel to the fuel rail. A check valve is disposed between the high-pressure pump and the fuel rail. The check valve leads fuel to flow from the high-pressure pump to the fuel rail. A fuel-pressure control valve is disposed in a fuel bypass line communicating between an output port of the high-pressure pump and an input port of the high-pressure pump. The fuel-pressure control valve selectively opens and closes the fuel bypass line. A controller is also provided for opening and closing operation of the fuel-pressure control valve on the basis of fuel injection timing, an amount of fuel injected and a delay time of the fuel-pressure control valve such that fuel pressure inside said fuel rail approaches an optimal fuel pressure.
Preferably, the fuel pressure inside the fuel rail is detected by a pressure sensor that is mounted to the fuel rail. The optimal fuel pressure is calculated by the controller on the basis of engine speed and engine load.
In a further preferred embodiment, a fuel line is adapted to provide pressurized fuel to a fuel rail supporting fuel injectors. A fuel pump having an input and an output is disposed in the fuel line. A check valve is disposed in the fuel line down stream from the pump. A bypass line communicates between the pump output and input. A fuel-pressure control valve is disposed in the bypass line. The pressure is controlled by a control unit communicating with the fuel-pressure control valve. The control unit generates a signal for selectively opening or closing the fuel-pressure control valve based on fuel injection timing, an amount of fuel injected and a delay time of the fuel-pressure control valve such that fuel pressure inside the fuel rail approaches an optimal fuel pressure. Preferably, the system further comprises an engine speed sensor and a engine load sensor communicating with the control unit. The control unit thus calculates the optimal fuel pressure based on input from the sensors.
In another preferred embodiment of the present invention, a fuel injection control method comprises a number of steps, including monitoring engine operating conditions and determining various parameters. For example, an optimal fuel injection pressure may be determined on the basis of the monitored engine operating conditions. Also, on/off timing and on/off duration of the fuel-pressure control valve may be determined such that fuel pressure inside a fuel rail approaches optimal fuel injection pressure. The fuel-pressure control valve may then be opened and closed according to the determined on/off timing and on/off duration of said fuel-pressure control valve.
Preferably, the on/off timing and on/off duration of the fuel-pressure control valve is determined on the basis of injection timing, an amount of fuel injected, and a delay time of said fuel-pressure control valve. Further preferably, the engine operating conditions include at least one of engine speed and engine load, and the fuel pressure inside said fuel rail is detected by a pressure sensor mounted to said fuel rail. The fuel injection control method of the invention may further comprise determining if the engine is starting, and maintaining the fuel-pressure control valve closed for a predetermined duration if it is determined that the engine is starting.
In a further preferred embodiment, the method may be executed using a system comprising a high-pressure pump pump for pumping fuel, a fuel-pressure control valve disposed in a fuel bypass line communicating an output port of said high-pressure pump and an input port of said high-pressure pump, said fuel-pressure control valve selectively opening and closing said fuel bypass, and a controller for controlling said fuel-pressure control valve in order to regulate fuel pressure.